Multiple reactivations along the eastern border fault of the Hartford basin
- Indiana Univ., Bloomington, IN (United States). Dept. of Geological Sciences
Multiple generations of deformation from the high grade ductile to the low grade brittle regime have been identified along the eastern border fault of the southern Hartford basin. Blastonylonitic schists that cut gneisses of the Bronson Hill terrane define ductile shear zones containing fibrolite, biotite, feldspar and retrograde muscovite after sillimanite + K-feldspar. Fibrolite defines a strong lineation plunging gently down dip to the NW. These upper amphibolite facies shear zones are reactivated under greenschist facies conditions, where mylonites and foliated cataclasites, also dipping gently to the NW, cut the higher grade shear zones. The mylonites contain a strong foliation defined by muscovite-biotite [plus minus] chlorite rich (P) domains separating quartz-feldspar-biotite (Q) domains. The layering established by the alternating P and Q domains is deformed into asymmetric and locally overturned folds verging NW. Layered mylonites are in turn cut by gentle northwest dipping cataclasites. Within the cataclasites randomly orientated porphyroclasts of muscovite, quartz, and feldspar float in a fine grained matrix dominated by muscovite and including biotite and minor chlorite. All of the above rocks and structures are cut by brittle faults. Some reactivate the earlier low angle shear zones, which display northwest plunging slickensides. Others cut these structures at higher angles, and dip more steeply to the northwest; slickensides still plunge dominantly down dip. Some brittle faults are breccia zones up to 1 m wide, with slickensided and rotated blocks indicating normal motion. This spectrum of conditions of faulting, from the upper amphibolite facies ductile shear zones to sub-greenschist facies brittle deformation indicates a protracted history of deformation on this boundary, certainly extending back into the Permian.
- OSTI ID:
- 5934595
- Report Number(s):
- CONF-9303211-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:2; Conference: 28. annual Geological Society of America (GSA) Northeastern Section meeting, Burlington, VT (United States), 22-24 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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